In recent years, data center and cloud computing technologies are developed rapidly. Compared with a conventional computing mode, cloud computing has an unparalleled advantage in aspects such as reliability and scalability. More and more enterprises and individuals choose to store their own data in a storage system of a cloud computing network. At the same time, applications of the data center and cloud computing technologies also bring new challenges. A main challenge is that an owner of data and a manager of data are no longer a same party, and an enterprise or an individual, as the owner of the data, stores the data in the storage system of the cloud computing network, while the cloud computing network becomes the manager of the data. On the one hand, a user (the owner of data) expects to make use of computing, storing, and communication capabilities of the cloud computing network to finish a lot of work; on the other hand, the user does not completely trust the cloud computing network. Therefore, efforts are always made in the industry to seek a method for protecting data of a data owner from being illegally obtained.